Use of lubricants with carboxylic acid esters in electric vehicles

ABSTRACT

The present invention relates to a use of a lubricant comprising a base oil selected from a carboxylic acid ester in an electric vehicle. It further relates to a method for lubricating an electric vehicle with a lubricant comprising the carboxylic acid ester.

The present invention relates to a use of a lubricant comprising a base oil selected from a carboxylic acid ester in an electric vehicle. It further relates to a method for lubricating an electric vehicle with a lubricant comprising the carboxylic acid ester. Combinations of preferred embodiments with other preferred embodiments are within the scope of the present invention.

A major challenge in lubricating electric vehicles is controlling lubricant electrical conductivity over the lifetime of the lubricant while meeting wear protection, oxidation stability, deposit control, and corrosion inhibition requirements. At the same time oil-derived lubricating properties must be maintained despite exposure to high surface temperatures of electrical components in electric and hybrid vehicles. A base oil with a high heat conductivity is desirable and would allow to transport away the heat of the hot surfaces. As the same time lubricant electrical conductivity and heat conductivity should be balanced with lubricant stability and many other lubricant properties such as low viscosity and achieving good gear protection.

The electric conductivity of the lubricant should be in a certain range. In case it is too high an electrical charge leakage and drain down of energy storage devices, such as for example batteries, may occur in the electrified systems of electric vehicles. In case the electric conductivity is too low electrostatic uploading of parts may occur. Various lubricant additives are know for adjusting the conductivity of the base oil of the lubricant.

There exists a need for a vehicle lubricant having desired lubricant electrical conductivity over the lifetime of the lubricant in combination with heat conductivity, wear protection, oxidation stability, deposit control, corrosion inhibition, and compatibility with electric vehicle mechanical and electrical components and materials over a broad temperature range. Further object was to find a base oil which requires less or no additives to adjust the electric conductivity.

The objects were achieved by a use of a lubricant comprising a base oil selected from a carboxylic acid ester in an electric vehicle.

The objects were also achieved by a method for lubricating an electric vehicle with a lubricant comprising a carboxylic acid ester.

Preferably the carboxylic acid ester is a monoester, diester, polyester, complex ester, or mixture thereof. The carboxylic acid ester is more preferred a diester, polyester, or complex esters. The carboxylic acid ester may comprise a mixture of different carboxylic acid esters.

The carboxylic acid esters may comprise aliphatic, aromatic, or a mixture of aliphatic and aromatic alcohols and/or acids. In one form the carboxylic acid esters consists of aliphatic alcohols and aliphatic acids. In another form the carboxylic acid esters consists of aliphatic alcohols and aliphatic and/or aromatic acids.

The carboxylic acid esters may comprise saturated, unsaturated or a mixture of saturated and unsaturated alcohols and/or acids. In one form the carboxylic acid esters may comprise saturated alcohols and saturated acids. In one form the carboxylic acid esters may comprise saturated alphatic alcohols and saturated aliphatic acids.

Suitable carboxylic acid ester are obtainable by reacting

-   -   (i) at least one linear or branched C₂-C₂₄ monocarboxylic acid         with at least one linear or branched C₁-C₂₀ monoalcohol (also         called “monoester”) or;     -   (ii) at least one linear or branched C₂-C₂₀ dicarboxylic acid         with at least one linear or branched C₁-C₂₀ monoalcohol (also         called “diester”) or;     -   (iii) at least one linear or branched C₂-C₂₄ monocarboxylic acid         with at least one C₂-C₂₀ polyol having 2-10 hydroxyl group (also         called “polyester”) or;     -   (iv) a mixture comprising at least one linear or branched C₂-C₂₄         monocarboxylic acid and at least one linear or branched C₂-C₂₀         dicarboxylic acid and at least one C₂-C₂₀ polyol having 2-10         hydroxyl group (also called “complex ester”) or;     -   (v) at least one linear or branched C₂-C₂₀ dicarboxylic acid         with at least one C₂-C₂₀ polyol having 2-10 hydroxyl group or;     -   (vi) a mixture comprising at least one linear or branched C₂-C₂₄         monocarboxylic acid and at least one linear or branched C₂-C₂₀         dicarboxylic acid and at least one linear or branched C₁-C₂₀         monoalcohol or;     -   (vii) a mixture comprising at least one linear or branched         C₂-C₂₄ monocarboxylic acid and at least one linear or branched         C₂-C₂₀ dicarboxylic acid and at least one C₂-C₂₀ polyol having         2-10 hydroxyl group and at least one C₁-C₂₀ monoalcohol.

In a more preferred embodiment the carboxylic acid ester is obtainable by reacting

-   -   (i) at least one linear or branched C₂-C₂₄ monocarboxylic acid         with at least one linear or branched C₁-C₂₀ monoalcohol (also         called “monoester”) or;     -   (ii) at least one linear or branched C₂-C₂₀ dicarboxylic acid         with at least one linear or branched C₁-C₂₀ monoalcohol (also         called “diester”) or;     -   (iii) at least one linear or branched C₂-C₂₄ monocarboxylic acid         with at least one C₂-C₂₀ polyol having 2-10 hydroxyl group (also         called “polyester”) or;     -   (iv) a mixture comprising at least one linear or branched C₂-C₂₄         monocarboxylic acid and at least one linear or branched C₂-C₂₀         dicarboxylic acid and at least one C₂-C₂₀ polyol having 2-10         hydroxyl group (also called “complex ester”).

In one form the carboxylic acid ester is a monoester obtainable by reacting

-   -   at least one linear or branched C₅-C₂₀ monocarboxylic acid         selected from the group consisting of pentanoic acid,         iso-pentanoic acid, hexanoic acid, iso-hexanoic acid, heptanoic         acid, iso-heptanoic acid, octanoic acid, iso-octanoic acid,         nonanoic acid, iso-nonanoic acid, decanoic acid, undecanoic         acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid,         pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic         acid, oleic acid, linoleic acid, linolenic acid, nonadecanoic         acid, eicosanoic acid with     -   at least one linear or branched C₁-C₁₈ monoalcohol selected from         the group consisting of methanol, ethanol, propanol, butanol,         pentanol, hexanol, heptanol, 1-octanol, 3-methyl-1-butanol,         nonanol, decanol, undecanol, dodecanol, tridecanol,         tetradecanol, pentadecanol, hexadecanol, heptadecanol,         octadecanol, iso-propanol, iso-butanol, 2-octanol, 3-octanol,         iso-nonanol, iso-decanol, iso-undecanol, iso-dodecanol         iso-tridecanol, iso-tetradecanol, iso-pentadecanol,         iso-hexadecanol, iso-heptadecanol, iso-octadecanol,         neo-pentanol, t-butanol, 2-methyl-2-butanol,         2,3-dimethyl-2-butanol, 2-methyl-2-pentanol,         3-methyl-3-pentanol, 3-ethyl-3-pentanol,         2,3-dimethyl-2-pentanol, 2,3-dimethyl-2-pentanol,         2,3-dimethyl-2-pentanol, 2,3-dimethyl-3-pentaol,         2,3,4-tri-methyl-3-pentanol, 2-methyl-2-hexanol and         3-methyl-3-hexanol.

In another form the monoester is obtainable by reacting at least one linear or branched C₁₂-C₂₀ monocarboxylic acid with at least one linear or branched C₆-C₁₆ monoalcohol. In another form the monoester is obtainable by reacting at least one linear or branched C₄-C₁₈ monocarboxylic acid with at least one linear or branched C₆-C₁₂ monoalcohol.

Examples for monosters are 2-ethylhexyl oleate, 2-ethylhexyl cocoate, 2-ethylhexyl palmitate, 2-ethylhexylstearate, and 2-ethylhexyl tallowate.

In another form the carboxylic acid ester is a diester obtainable by reacting

-   -   at least one linear or branched C₃-C₁₂ dicarboxylic acid         selected from the group consisting of malonic acid, succinic         acid, glutaric acid, adipic acid, maleic acid, fumaric acid,         azelaic acid, sebacic acid, brassilic acid, docdecanedioic acid,         diglycolic acid, 1,4-cyclohexanedicarboxylic acid,         1,3-cyclohexanedicarboxylic acid and         2,6-decahydro-naphthalenedicarboxylic acid with     -   at least one branched C₅-C₁₄ monoalcohol selected from the group         consisting of pentanol, hexanol, heptanol, iso-pentanol,         iso-hexanol, iso-heptanol, 2-ethylhexanol, 2-propylheptanol,         2-propyl-4-methyl-hexanol, 2-propyl-5-methyl-hexanol,         2-isopropyl-4-methyl-hexanol, 2-isopropyl-5-methyl-hexanol,         2-propyl-4,4-dimethylpentanol, 2-ethyl-2,4-dimethylhexanol,         2-ethyl-2-methyl-heptanol, 2-ethyl-2,5-dimethylhexanol,         2-iso-propylheptanol, 2-butyl-1-octanol and 2-pentyl-1-nonanol.

In one form the diesters are obtainable by reacting at least one linear or branched C₄-C₈ dicarboxylic acid with at least one branched C₆-C₁₆ monoalcohol. In one form the diesters are obtainable by reacting at least one linear or branched C₆-C₈ dicarboxylic acid with at least one branched C₆-C₁₄ monoalcohol. Examples for diesters are diisodecyl adipate, diisotridecyl adipate, di-(isopropylheptyl)-adipate (DPHA) and diisononyladipate (DNA).

Also suitable as diester is a dicarboxylic acid ester component which is formed from a dicarboxylic acid selected from the list consisting of adipic acid, phthalic acid, pimilic acid, suberic acid, azelaic acid and sebacic acid, and mixtures thereof and a branched aliphatic alcohol R—OH which is defined according to the following formula (I)

whereas q, r and s are q+r=4 to 9, s=0 to 5, q=1 to 8, and r=1 to 6.

Preferably, the branched aliphatic alcohol R—OH according to formula (I) can be a primary C₇ to C₁₂ alcohol, wherein the alkyl side chain is C₁ to C₆ alkyl (s=0 to 5). The alkyl side chain can be linear or branched alkyl group while linear alkyl group is preferred for the alkyl side chain.

Accordingly, the main alkyl chain in residue R is C₆ to C₁₁. Accordingly, the residue R in R—OH of formula (I) includes methylhexyl, ethylhexyl, propylhexyl, butylhexyl, pentylhexyl and hexylhexyl, methylheptyl, ethylheptyl, propylheptyl, butylheptyl and pentylheptyl, methyloctyl, ethyloctyl, propyloctyl, and butyloctyl, methylnonyl, ethylnonyl, and propylnonyl, methyldecyl and ethyldecyl, and methylundecyl. Especially preferred alcohols R—OH from the above list include residue R being ethylhexyl, methyloctyl, propylheptyl and butyloctyl. Most preferably, the residue R in R—OH in the above lubricant composition is selected from ethylhexyl, methyloctyl, propylheptyl, butyloctyl and mixtures thereof defined by q, r and s as follows:

R in R—OH of formula (I) Ethylhexyl q + r = 4 s = 1 q = 1 r = 3 q = 2 r = 2 q = 3 r = 1 Methyloctyl q + r = 6 s = 0 q = 1 r = 5 q = 2 r = 4 q = 3 r = 3 q = 4 r = 2 q = 5 r = 1 Propylheptyl q + r = 5 s = 2 q = 1 r = 4 q = 2 r = 3 q = 3 r = 2 q = 4 r = 1 Butyloctyl q + r = 6 s = 3 q = 1 r = 5 q = 2 r = 4 q = 3 r = 3 q = 4 r = 2 q = 5 r = 1

Especially preferred are the alcohols having q+r=4 to 9, r=1 and q=3 to 8, i.e. the primary aliphatic C₇ to C₁₂ alcohols in which the linear (which is preferred) or branched alkyl side chain C₁ to C₆ alkyl (s=0 to 5) is located at the 2-position of the primary alcohol. Such alcohols are typically named Guerbet alcohols. In one preferred embodiment the Guerbet alcohol is derived at least partly from 2-hexyl decanol, 2-hexyl dodecanol, 2-octyl decanol and/or 2-octyl dodecanol.

The dicarboxylic ester preferably is derived from the reaction of a dicarboxylic acid with an aliphatic alcohol. Preferred dicarboxylic acids are adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid and mixtures thereof. The dicarboxylic acid ester component is preferably formed from such dicarboxylic acids by esterification with medium-size aliphatic alcohols, which can be linear or branched, preferably C₅ to C₂₀ alcohol, more preferably C₉ to C₁₅ aliphatic alcohol and most preferably nonanol, isodecanol, isotridecanol and 2-propyl heptanol.

In another form the carboxylic acid ester is a polyester obtainable by reacting

-   -   at least one linear or branched C₅-C₁₈ monocarboxylic acid         selected from the group consisting of pentanoic acid, caproic         acid, heptanoic acid, caprylic acid, nonanoic acid capric acid,         undecanoic acid, dodecanoic acid, tridecanoic acid,         tetradecanoic acid, pentadecanoic acid, hexadecanoic acid,         heptadecanoic acid, octadecanoic acid, oleic acid, palmitoleic         acid with     -   at least one C₂-C₂₀ polyol having 2-10 hydroxyl group selected         from the group consisting of ethylene glycol, 1,2-propylene         glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene         glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol         propane, trimethylol ethane, pentaerythritol, sorbitol, and         dipentaerythritol.

In another form the polyester are obtainable by reacting at least one linear or branched C₈-C₁₈ monocarboxylic acid with at least one C₃-C₁₆ polyol having 3-6 hydroxyl group. In another form the polyester are obtainable by reacting at least one linear or branched C₁₄-C₁₈ monocarboxylic acid with at least one C₄-C₁₂ polyol having 3-5 hydroxyl group.

Examples for polyesters are trimethylolpropane-type ester, preferably formed from TMP with C₅-C₁₈ aliphatic monoacids, e.g. trimethylolpropane caprylate (TMTC) and trimethylolpropane-trioleate. Further examples for polyesters are pentaerythrit-type ester, preferably formed from pentaerythrit with C₅-C₁₈ aliphatic monoacids.

In another form the carboxylic acid ester is a complex ester obtainable by reacting a mixture comprising

-   -   at least one linear or branched C₅-C₁₈ monocarboxylic acid         selected from the group consisting of pentanoic acid, caproic         acid, heptanoic acid, caprylic acid, nonanoic acid capric acid,         undecanoic acid, dodecanoic acid, tridecanoic acid,         tetradecanoic acid, pentadecanoic acid, hexadecanoic acid,         heptadecanoic acid, octadecanoic acid, oleic acid, palmitoleic         acid and     -   at least one linear or branched C₃-C₁₀ dicarboxylic acid         selected from the group consisting of malonic acid, succinic         acid, glutaric acid, adipic acid, heptanedioic acid,         octananedioic acid, nonanedioic acid, decanedioic acid and     -   at least one C₂-C₂₀ polyol having 2-10 hydroxyl group selected         from the group consisting of ethylene glycol, 1,2-propylene         glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene         glycol, 2,3-butylene glycol neopentyl glycol, trimethylol         propane, trimethylol ethane, pentaerythritol, sorbitol, and         dipentaerythritol.

In another form the complex ester are obtainable by reacting a mixture comprising

-   -   at least one linear or branched C₆-C₁₈ monocarboxylic acid and     -   at least one linear or branched C₄-C₁₀ dicarboxylic acid and     -   at least one C₂-C₁₄ polyol having 2-6 hydroxyl group.

In another form the complex ester are obtainable by reacting a mixture comprising

-   -   at least one linear or branched C₁₂-C₁₈ monocarboxylic acid and     -   at least one linear or branched C₆-C₈ dicarboxylic acid and     -   at least one C₃-C₁₀ polyol having 3-5 hydroxyl group.

Suitable electric vehicles are fully electric vehicles and hybrid electric vehicles. An electric vehicle usually comprises a rotary electric machine and an electric power storage device configured to store electric power that is used to drive the rotary electric machine. A hybrid electric vehicle usually travels by using power of a rotary electric machine and a combustion engine.

Suitable hybrid electric vehicles are full hybrid (also called strong hybrid), plug-in hybrid (also called PHEV) electric vehicles, or range extended electric vehicles (also called REEV). A full hybrid electric vehicle is typically a vehicle that can run only on a combustion engine, only on an electric motor, or a combination of both. A plug-in hybrid electric vehicle is typically a hybrid electric vehicle with rechargeable batteries that can be restored to full charge by connecting a plug to an external electric power source.

Suitable electric vehicles are battery electric vehicles (also called BEV) or fuel cell electric vehicles. A BEV is typically a type of electric vehicle that uses chemical energy stored in rechargeable battery packs, and uses electric motors and motor controllers instead of internal combustion engines for propulsion. A fuel cell electric vehicle (FCEV) is typically a type of electric vehicle which uses a fuel cell, instead of a battery, or in combination with a battery or supercapacitor, to power its on-board rotary electric machine. Fuel cells in vehicles generate electricity to power the motor, generally using oxygen from the air and compressed hydrogen.

The term “vehicle” refers to any mobile or stationary platform, wherein mobile platforms are preferred. In particular vehicles are selected from a passenger vehicle, a light-duty or heavy-duty truck, a utility vehicle, an agricultural vehicle, an industrial or warehouse vehicle, or a recreational off-road vehicle.

The lubrication of electric vehicles may refer to lubrication of powertrains, drivelines, transmissions, differentials, gears, gear trains, gear sets, gear boxes, bearings, bushings, axles, turbines, compressors, pumps, hydraulic systems, batteries, capacitors, electric motors, drive motors, generators, AC/DC converters, alternators, transformers, kinetic energy converters, kinetic energy recovery systems. A single lubricant or more than one lubricant may be used in the electric vehicle, for example, one lubricant composition for the transmission and another lubricant composition for another component of the vehicle system.

The lubricant may lubricate various surfaces of electric vehicles, that include, for example, the following: metals, metal alloys, non-metals, non-metal alloys, mixed carbon-metal composites and alloys, mixed carbon-nonmetal composites and alloys, ferrous metals, ferrous composites and alloys, non-ferrous metals, non-ferrous composites and alloys, titanium, titanium composites and alloys, aluminum, aluminum composites and alloys, magnesium, magnesium composites and alloys, ion-implanted metals and alloys, plasma modified surfaces; surface modified materials; coatings; mono-layer, multi-layer, and gradient layered coatings; honed surfaces; polished surfaces; etched surfaces; textured surfaces; micro and nano structures on textured surfaces; super-finished surfaces; diamond-like carbon (DLC), DLC with high-hydrogen content, DLC with moderate hydrogen content, DLC with low-hydrogen content, DLC with near-zero hydrogen content, DLC composites, DLC-metal compositions and composites, DLC-nonmetal compositions and composites; ceramics, ceramic oxides, ceramic nitrides, FeN, CrN, ceramic carbides, mixed ceramic compositions, cermets, and the like; polymers, thermoplastic polymers, engineered polymers, polymer blends, polymer alloys, polymer composites; materials compositions and composites containing dry lubricants, that include, for example, graphite, carbon, molybdenum, molybdenum disulfide, polytetrafluoroethylene, polyperfiuoropropylene, polyperfluoroalkylethers, and the like; super hydrophobic surfaces; super hydrophilic surfaces; self-healing surfaces; surfaces derived from 3-D printing or additive manufacturing techniques, which may be additionally used as -manufactured, or used with post-printing surface finishing, or used with post-printing surface coating.

In one form the lubricant is present within the rotary electric machine of the electric vehicle.

In another form the lubricant is present outside in close distance to the rotary electric machine of the electric vehicle, and usually onboard of the electric vehicle. Preferably, the lubricant is present outside the rotary electric machine in direct contact with it or within a distance of up to 300, 250, 200, 150, 100, 50, 40, 30, 20 or 10 cm. Examples for the lubricant being present outside the rotary electric machine are lubricants present in powertrains, drivelines, transmissions, differentials, gears, gear trains, gear sets, gear boxes, bearings, bushings, axles, turbines, compressors, pumps, hydraulic systems, batteries, capacitors, generators, AC/DC converters, alternators, transformers, kinetic energy converters, or kinetic energy recovery systems.

The heat conductivity of the the carboxylic acid ester (preferably at 90° C.) may be at least 0.120, 0.125, 0.130, 0.131, 0.132, 0.133, 0.135, 0.137, 0.139, 0.141, 0.143, 0.145, or 0.147 W/mK.

The heat conductivity (preferably at 90° C.) of the carboxylic acid ester may be up to 0.3, 0.2, 0.17, or 0.15 W/mK.

The heat conductivity may be determined with the stationary cylinder gap method: The base oils is located between two cylindrical metal bodies with spherical ends with a gap of one millimeter. The outer cylinder is surrounded by a thermostat fluid, which keeps the temperature of the measuring device constant. The temperature is measured both in the inner cylinder and in the outer cylinder. After reaching thermal equilibrium at a constant temperature, the inner cylinder is heated up by a defined power by maximum 0.5 K. The temperature difference between outer and inner cylinder is thus only dependent on the thermal conductivity of the fluid and on the heating power. This temperature difference is measured twice at two different heating power levels. The measurement of the thermal conductivity of the base oils was done in the temperature range from 30 to 90° C. at three different temperatures.

The heat conductivity may also be determined according to ASTM D7896-19 “Standard Test Method for Thermal Conductivity, Thermal Diffusivity, and Volumetric Heat Capacity of Engine Coolants and Related Fluids by Transient Hot Wire Liquid Thermal Conductivity Method”.

The thermo-oxidative stability of the carboxylic acid ester may be determined by High Pressure Differential Scanning Calorimetry (HP-DSC). HP-DSC is a technique used to accelerate oxidative stability testing. In the presence of air or oxygen, lubricants will degrade through oxidation. At ambient temperature and atmospheric pressure oxidation is almost immeasurably slow but the rate of oxidation strongly increases with temperature.

The HP-DCS may be tested as follows: About 1 mg of a sample was heated from 30 to 400° C. with 5K/min in an open aluminum pot under 10 bar pure oxygen atmosphere. The HP-DCS is given in degree Celsius of the onset temperature or the peak temperature (preferably the onset temperature) and the higher the value the better the thermo-oxidative stability.

The thermo-oxidative stability of the carboxylic acid ester according to HP-DSC may be at least 130, 150, 170, 180 or 190° C. onset temperature. The thermo-oxidative stability according to HP-DSC may be up to 300, 280, 260 or 240° C. onset temperature.

The thermo-oxidative stability of the carboxylic acid ester according to HP-DSC may be at least 130, 150, 170, 180, 190, 200, 210 or 220° C. peak temperature. The thermo-oxidative stability according to HP-DSC may be up to 300, 280, 260 or 240° C. peak temperature.

The thermo-oxidative stability may also be determined according to ASTM D943 (“Standard Test Method for OxidationCharacteristics of Inhibited Mineral Oils”), also known as Turbine Oil Oxidation Stability Test TOST. The TOST for the carboxylic acid esters may be determined in the absence of water. The TOST values for the carboxylic acid esters are usually at least 4000, 6000, 7000, 8000, 9000 or 10000 hours. The increase in acid number is usually at least 2 mg KOH/g.

The electrical conductivity of the carboxylic acid ester may be at least 0.01, 0.1, 0.5, 1, 5, 10, 30, 50, or 100 pS/m.

The electrical conductivity of the carboxylic acid ester may be up to 100 000, 50 000, 10 000, 5000, 1000, or 500 pS/m.

The The electrical conductivity of the carboxylic acid ester may be in the range from 0.1 to 100 000 pS/m, 1 to 50 000 pS/m, 1 to 10 000 pS/m, 10 to 5000 pS/m, 10 to 1000 pS/m, 10 to 500 pS/m or 30 to 300 pS/m.

The electrical conductivity may be determined preferably according to ASTM D2624 “Standard Test Methods for Electrical Conductivity of Aviation and Distillate Fuels”, typically at 25° C. In another form the electrical conductivity may be determined according to ASTM D4308 “Standard Test Method for Electrical Conductivity of Liquid Hydrocarbons by Precision Meter”, typically at 25° C.

The term “lubricants” usually refers to composition which are capable of reducing friction between surfaces (preferably metal surfaces), such as surfaces of mechanical devices. A mechanical device may be a mechanism consisting of a device that works on mechanical principles. The lubricant is usually a lubricating liquid, lubricating oil or lubricating grease.

The lubricant usually further comprises in addition to the base oil selected from carboxylic acid esters

-   -   a further base oil selected from mineral oils, polyalphaolefins,         polymerized and interpolymerized olefins, alkyl naphthalenes,         alkylene oxide polymers, silicone oils, phosphate ester; and/or     -   a lubricant additive.

The further base oil may selected from the group consisting of mineral oils (Group I, II or III oils), polyalphaolefins (Group IV oils), polymerized and interpolymerized olefins, alkyl naphthalenes, alkylene oxide polymers, silicone oils, phosphate esters (Group V oils). Preferably, the further base oil is selected from Group I, Group II, Group III base oils according to the definition of the API, or mixtures thereof. Definitions for the base oils are the same as those found in the American Petroleum Institute (API) publication “Engine Oil Licensing and Certification System”, Industry Services Department, Fourteenth Edition, December 1996, Addendum 1, December 1998. Said publication categorizes base oils as follows:

-   -   a) Group I base oils contain less than 90 percent saturates         (ASTM D 2007) and/or greater than 0.03 percent sulfur (ASTM         D 2622) and have a viscosity index (ASTM D 2270) greater than or         equal to 80 and less than 120.     -   b) Group I base oils contain greater than or equal to 90 percent         saturates and less than or equal to 0.03 percent sulfur and have         a viscosity index greater than or equal to 80 and less than 120.     -   c) Group III base oils contain greater than or equal to 90         percent saturates and less than or equal to 0.03 percent sulfur         and have a viscosity index greater than or equal to 120.     -   d) Group IV base oils contain polyalphaolefins. Polyalphaolefins         (PAO) include known PAO materials which typically comprise         relatively low molecular weight hydrogenated polymers or         oligomers of alphaolefins which include but are not limited to         C2 to about C32 alphaolefins with the C8 to about C16         alphaolefins, such as 1-octene, 1-decene, 1-dodecene and the         like being preferred. The preferred polyalphaolefins are         poly-1-octene, poly-1-decene, and poly-1-dodecene.     -   e) Group V base oils contain any base oils not described by         Groups I to IV. Examples of Group V base oils include alkyl         naphthalenes, alkylene oxide polymers, silicone oils, and         phosphate esters.

Synthetic base oils include hydrocarbon oils and halo-substituted hydrocarbon oils such as polymerized and interpolymerized olefins (e.g., polypropylenes, propylene-isobutylene copolymers, chlorinated polybutylenes, poly(1-hexenes), poly(1-octenes), poly(1-decenes)); alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes, dinonylbenzenes, di(2-ethylhexyl)benzenes); poly-phenyls (e.g., biphenyls, terphenyls, alkylated polyphenols); and alkylated diphenyl ethers and alkylated diphenyl sulfides and derivative, analogs and homologs thereof.

Alkylene oxide polymers and interpolymers and derivatives thereof where the terminal hydroxyl groups have been modified by esterification, etherification, etc., constitute another class of known synthetic base oils. These are exemplified by polyoxyalkylene polymers prepared by polymerization of ethylene oxide or propylene oxide, and the alkyl and aryl ethers of polyoxyalkylene polymers (e.g., methyl-polyisopropylene glycol ether having a molecular weight of 1000 or diphenyl ether of polyethylene glycol having a molecular weight of 1000 to 1500); and mono- and polycarboxylic esters thereof, for example, the acetic acid esters, mixed C3-C8 fatty acid esters and C13 oxo acid diester of tetraethylene glycol.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy- or polyaryloxysilicone oils and silicate oils comprise another useful class of synthetic base oils; such base oils include tetraethyl silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl)silicate, tetra-(4-methyl-2-ethylhexyl) silicate, tetra-(p-tert-butyl-phenyl) silicate, hexa-(4-methyl-2-ethylhexyl)disiloxane, poly(methyl) siloxanes and poly(methylphenyl)siloxanes. Other synthetic base oils include liquid esters of phosphorous-containing acids (e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of decylphosphonic acid) and polymeric tetrahydrofurans.

Suitable lubricant additives may be selected from viscosity index improvers, polymeric thickeners, corrosion inhibitors, detergents, dispersants, anti-foam agents, dyes, wear protection additives, extreme pressure additives (EP additives), anti-wear additives (AW additives), friction modifiers, metal deactivators, pour point depressants.

The viscosity index improvers include high molecular weight polymers that increase the relative viscosity of an oil at high temperatures more than they do at low temperatures. Viscosity index improvers include polyacrylates, polymethacrylates, alkylmethacrylates, vinylpyrrolidone/meth-acrylate copolymers, poly vinylpyrrolidones, polybutenes, olefin copolymers such as an ethylene-propylene copolymer or a styrene-butadiene copolymer or polyalkene such as PIB, styrene/acrylate copolymers and polyethers, and combinations thereof.

The most common VI improvers are methacrylate polymers and copolymers, acrylate polymers, olefin polymers and copolymers, and styrenebutadiene copolymers. Other examples of the viscosity index improver include polymethacrylate, polyisobutylene, alpha-olefin polymers, alpha-olefin copolymers (e.g., an ethylenepropylene copolymer), polyalkylstyrene, phenol condensates, naphthalene condensates, a styrenebutadiene copolymer and the like. Of these, polymethacrylate having a number average molecular weight of 10000 to 300000, and alpha-olefin polymers or alpha-olefin copolymers having a number average molecular weight of 1000 to 30000, particularly ethylene-alpha-olefin copolymers having a number average molecular weight of 1000 to 10000 are preferred. The viscosity index increasing agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from ≥0.05 to ≤20.0% by weight, in relation to the weight of the base stock.

Suitable (polymeric) thickeners include, but are not limited to, polyisobutenes (PIB), oligomeric co-polymers (OCPs), polymethacrylates (PMAs), copolymers of styrene and butadiene, or high viscosity esters (complex esters).

Corrosion inhibitors may include various oxygen-, nitrogen-, sulfur-, and phosphorus-containing materials, and may include metal-containing compounds (salts, organometallics, etc.) and nonmetal-containing or ashless materials. Corrosion inhibitors may include, but are not limited to, additive types such as, for example, hydrocarbyl-, aryl-, alkyl-, arylalkyl-, and alkylaryl-versions of detergents (neutral, overbased), sulfonates, phenates, salicylates, alcoholates, carboxylates, salixarates, phosphites, phosphates, thiophosphates, amines, amine salts, amine phosphoric acid salts, amine sulfonic acid salts, alkoxylated amines, etheramines, polyetheramines, amides, imides, azoles, diazoles, triazoles, benzotriazoles, benzothiadoles, mercaptobenzothiazoles, tolyltriazoles (TTZ-type), heterocyclic amines, heterocyclic sulfides, thiazoles, thiadiazoles, mercaptothiadiazoles, dimercaptothiadiazoles (DMTD-type), imidazoles, benzimidazoles, dithiobenzimidazoles, imidazolines, oxazolines, Mannich reactions products, glycidyl ethers, anhydrides, carbamates, thiocarbamates, dithiocarbamates, polyglycols, etc., or mixtures thereof.

Detergents include cleaning agents that adhere to dirt particles, preventing them from attaching to critical surfaces. Detergents may also adhere to the metal surface itself to keep it clean and prevent corrosion from occurring. Detergents include calcium alkylsalicylates, calcium alkylphenates and calcium alkarylsulfonates with alternate metal ions used such as magnesium, barium, or sodium. Examples of the cleaning and dispersing agents which can be used include metal-based detergents such as the neutral and basic alkaline earth metal sulphonates, alkaline earth metal phenates and alkaline earth metal salicylates alkenylsuccinimide and alkenylsuccinimide esters and their borohydrides, phenates, salienius complex detergents and ashless dispersing agents which have been modified with sulphur compounds. These agents can be added and used individually or in the form of mixtures, conveniently in an amount within the range of from ≥0.01 to ≤1.0% by weight in relation to the weight of the base stock; these can also be high total base number (TBN), low TBN, or mixtures of high/low TBN.

Dispersants are lubricant additives that help to prevent sludge, varnish and other deposits from forming on critical surfaces. The dispersant may be a succinimide dispersant (for example N-substituted long chain alkenyl succinimides), a Mannich dispersant, an ester-containing dispersant, a condensation product of a fatty hydrocarbyl monocarboxylic acylating agent with an amine or ammonia, an alkyl amino phenol dispersant, a hydrocarbyl-amine dispersant, a polyether dispersant or a polyetheramine dispersant. In one embodiment, the succinimide dispersant includes a polyisobutylene-substituted succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000, or of about 950 to about 1600. In one embodiment, the dispersant includes a borated dispersant. Typically, the borated dispersant includes a succinimide dispersant including a polyisobutylene succinimide, wherein the polyisobutylene from which the dispersant is derived may have a number average molecular weight of about 400 to about 5000. Borated dispersants are described in more detail above within the extreme pressure agent description.

Anti-foam agents may be selected from silicones, polyacrylates, and the like. The amount of anti-foam agent in the lubricant compositions described herein may range from ≥0.001 wt.-% to ≤0.1 wt.-% based on the total weight of the formulation. As a further example, an anti-foam agent may be present in an amount from about 0.004 wt.-% to about 0.008 wt.-%.

Suitable extreme pressure agent is a sulfur-containing compound. In one embodiment, the sulfur-containing compound may be a sulfurised olefin, a polysulfide, or mixtures thereof.

Examples of the sulfurised olefin include a sulfurised olefin derived from propylene, isobutylene, pentene; an organic sulfide and/or polysulfide including benzyldisulfide; bis-(chlorobenzyl) disulfide; dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurised methyl ester of oleic acid, a sulfurised alkylphenol, a sulfurised dipentene, a sulfurised terpene, a sulfurised Diels-Alder adduct, an alkyl sulphenyl N′N-dialkyl dithiocarbamates; or mixtures thereof. In one embodiment, the sulfurised olefin includes a sulfurised olefin derived from propylene, isobutylene, pentene or mixtures thereof. In one embodiment the extreme pressure additive sulfur-containing compound includes a dimercaptothiadiazole or derivative, or mixtures thereof. Examples of the dimercaptothiadiazole include compounds such as 2,5-dimercapto-1,3,4-thiadiazole or a hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole, or oligomers thereof. The oligomers of hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typically form by forming a sulfur-sulfur bond between 2,5-dimercapto-1,3,4-thiadiazole units to form derivatives or oligomers of two or more of said thiadiazole units. Suitable 2,5-dimercapto-1,3,4-thiadiazole derived compounds include for example 2,5-bis(tert-nonyldithio)-1,3,4-thiadiazole or 2-tert-nonyldithio-5-mercapto-1,3,4-thiadiazole. The number of carbon atoms on the hydrocarbyl substituents of the hydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typically include 1 to 30, or 2 to 20, or 3 to 16. Extreme pressure additives include compounds containing boron and/or sulfur and/or phosphorus. The extreme pressure agent may be present in the lubricant compositions at 0 wt.-% to about 20 wt.-%, or at about 0.05 wt.-% to about 10.0 wt.-%, or at about 0.1 wt.-% to about 8 wt.-% of the lubricant composition.

Examples of anti-wear additives include organo borates, organo phosphites such as didodecyl phosphite, organic sulfur-containing compounds such as sulfurized sperm oil or sulfurized terpenes, zinc dialkyl dithiophosphates, zinc diaryl dithiophosphates, phosphosulfurized hydrocarbons and any combinations thereof.

Friction modifiers may include metal-containing compounds or materials as well as ashless compounds or materials, or mixtures thereof. Metal-containing friction modifiers include metal salts or metal-ligand complexes where the metals may include alkali, alkaline earth, or transition group metals. Such metal-containing friction modifiers may also have low-ash characteristics. Transition metals may include Mo, Sb, Sn, Fe, Cu, Zn, and others. Ligands may include hydrocarbyl derivative of alcohols, polyols, glycerols, partial ester glycerols, thiols, carboxylates, carbamates, thiocarbamates, dithiocarbamates, phosphates, thiophosphates, dithiophosphates, amides, imides, amines, thiazoles, thiadiazoles, dithiazoles, diazoles, triazoles, and other polar molecular functional groups containing effective amounts of O, N, S, or P, individually or in combination. In particular, Mo-containing compounds can be particularly effective such as for example Mo-dithiocarbamates, Mo(DTC), Mo-dithiophosphates, Mo(DTP), Mo-amines, Mo (Am), Mo-alcoholates, Mo-alcohol-amides, and the like.

Ashless friction modifiers may also include lubricant materials that contain effective amounts of polar groups, for example, hydroxyl-containing hydrocarbyl base oils, glycerides, partial glycerides, glyceride derivatives, and the like. Polar groups in friction modifiers may include hydrocarbyl groups containing effective amounts of O, N, S, or P, individually or in combination. Other friction modifiers that may be particularly effective include, for example, salts (both ash-containing and ashless derivatives) of fatty acids, fatty alcohols, fatty amides, fatty esters, hydroxyl-containing carboxylates, and comparable synthetic long-chain hydrocarbyl acids, alcohols, amides, esters, hydroxy carboxylates, and the like. In some instances, fatty organic acids, fatty amines, and sulfurized fatty acids may be used as suitable friction modifiers. Examples of friction modifiers include fatty acid esters and amides, organo molybdenum compounds, molybdenum dialkylthiocarbamates and molybdenum dialkyl dithiophosphates.

Suitable metal deactivators include benzotriazoles and derivatives thereof, for example 4- or 5-alkylbenzotriazoles (e.g. triazole) and derivatives thereof, 4,5,6,7-tetrahydrobenzotriazole and 5,5′-methylenebisbenzotriazole; Mannich bases of benzotriazole or triazole, e.g. 1-[bis(2-ethylhexyl) aminomethyl) triazole and 1-[bis(2-ethylhexyl) aminomethyl)benzotriazole; and alkoxy-alkylbenzotriazoles such as 1-(nonyloxymethyl)benzotriazole, 1-(1-butoxyethyl) benzotriazole and 1-(1-cyclohexyloxybutyl) triazole, and combinations thereof. Additional non-limiting examples of the one or more metal deactivators include 1,2,4-triazoles and derivatives thereof, for example 3-alkyl(or aryl)-1,2,4-triazoles, and Mannich bases of 1,2,4-triazoles, such as 1-[bis(2-ethylhexyl) aminomethy1-1,2,4-triazole; alkoxyalky1-1,2,4-triazoles such as 1-(1-butoxyethyl)-1,2,4-triazole; and acylated 3-amino-1,2,4-triazoles, imidazole derivatives, for example 4,4′-methylenebis(2-undecyl-5-methylimidazole) and bis[(N-methyl)imidazol-2-yl]-carbinol octyl ether, and combinations thereof. Further non-limiting examples of the one or more metal deactivators include sulfur-containing heterocyclic compounds, for example 2-mercapto-benzothiazole, 2,5-dimercapto-1,3,4-thia-diazole and derivatives thereof; and 3,5-bis[di(2-ethylhexyl) aminomethyl]-1,3,4-thiadiazolin-2-one, and combinations thereof. Even further non-limiting examples of the one or more metal deactivators include amino compounds, for example salicylidenepropylenediamine, salicylami-noguanidine and salts thereof, and combinations thereof. The one or more metal deactivators are not particularly limited in amount in the composition but are typically present in an amount of from about 0.01 to about 0.1, from about 0.05 to about 0.01, or from about 0.07 to about 0.1, wt.-% based on the weight of the composition. Alternatively, the one or more metal deactivators may be present in amounts of less than about 0.1, of less than about 0.7, or less than about 0.5, wt.-% based on the weight of the composition.

Pour point depressants (PPD) include polymethacrylates, alkylated naphthalene derivatives, and combinations thereof. Commonly used additives such as alkylaromatic polymers and polymethacrylates are also useful for this purpose. Typically, the treat rates range from ≥0.001 wt.-% to ≤1.0 wt.-%, in relation to the weight of the base stock.

Demulsifiers include trialkyl phosphates, and various polymers and copolymers of ethylene glycol, ethylene oxide, propylene oxide, or mixtures thereof.

The lubricant may comprise at least 10, 20, 30, 40, 50, 60, 70, 80, 90, or 95 wt % of the carboxylic acid esters, e.g. as base oil.

The lubricant may comprise up to 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100 wt % of the carboxylic acid esters, e.g. as base oil.

In one form the lubricant is free of further base oil beside the carboxylic acid esters.

The lubricant can be prepared by contacting the base oil selected from carboxylic acid esters and optionally the further base oil and optionally the the lubricant additive. The contacting can be achieved by mixing, stirring, pouring in the desired amounts. 

1.-15. (canceled)
 16. A use of a lubricant comprising a base oil selected from a carboxylic acid ester in an electric vehicle.
 17. The use according to claim 16 where the electric vehicle comprises a rotary electric machine and an electric power storage device configured to store electric power that is used to drive the rotary electric machine.
 18. The use according to claim 16 where the lubricant is present within the rotary electric machine of the electric vehicle.
 19. The use according to claim 16 where the lubricant is present outside the rotary electric machine in direct contact with it or within a distance of up to 50 cm.
 20. The use according to claim 16 where the carboxylic acid ester has a electrical conductivity from 0.1 to 100 000 pS/m.
 21. The use according to claim 16 where the carboxylic acid ester has a heat conductivity of at least 0.120 W/mK.
 22. The use according to claim 16 where the carboxylic acid ester has a thermo-oxidative stability determined by high pressure differential scanning calorimetry of at least 130° C. onset temperature.
 23. The use according to claim 16 where the carboxylic acid ester is a monoester, diester, polyester, complex ester, or mixture thereof.
 24. The use according to claim 16 where the carboxylic acid ester is obtainable by reacting (i) at least one linear or branched C₂-C₂₄ monocarboxylic acid with at least one linear or branched C₁-C₂₀ monoalcohol (also called “monoester”) or; (ii) at least one linear or branched C₂-C₂₀ dicarboxylic acid with at least one linear or branched C₁-C₂₀ monoalcohol (also called “diester”) or; (iii) at least one linear or branched C₂-C₂₄ monocarboxylic acid with at least one C₂-C₂₀ polyol having 2-10 hydroxyl group (also called “polyester”) or; (iv) a mixture comprising at least one linear or branched C₂-C₂₄ monocarboxylic acid and at least one linear or branched C₂-C₂₀ dicarboxylic acid and at least one C₂-C₂₀ polyol having 2-10 hydroxyl group (also called “complex ester”).
 25. The use according to claim 16 where the carboxylic acid ester is a diester obtainable by reacting at least one linear or branched C₃-C₁₂ dicarboxylic acid selected from the group consisting of malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, azelaic acid, sebacic acid, brassilic acid, docdecanedioic acid, diglycolic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and 2,6-decahydro-naphthalenedicarboxylic acid with at least one branched C₅-C₁₄ monoalcohol selected from the group consisting of pentanol, hexanol, heptanol, iso-pentanol, iso-hexanol, iso-heptanol, 2-ethylhexanol, 2-propylheptanol, 2-propyl-4-methyl-hexanol, 2-propyl-5-methyl-hexanol, 2-isopropyl-4-methyl-hexanol, 2-isopropyl-5-methyl-hexanol, 2-propyl-4,4-dimethylpentanol, 2-ethyl-2,4-dimethylhexanol, 2-ethyl-2-methyl-heptanol, 2-ethyl-2,5-dimethylhexanol, 2-isopropyl-heptanol, 2-butyl-1-octanol and 2-pentyl-1-nonanol.
 26. The use according to claim 16 where the carboxylic acid ester is a polyester obtainable by reacting at least one linear or branched C₅-C₁₈ monocarboxylic acid selected from the group consisting of pentanoic acid, caproic acid, heptanoic acid, caprylic acid, nonanoic acid capric acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, oleic acid, palmitoleic acid with at least one C₂-C₂₀ polyol having 2-10 hydroxyl group selected from the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol, neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, sorbitol, and dipentaerythritol.
 27. The use according to claim 16 where the carboxylic acid ester is a complex ester obtainable by reacting a mixture comprising at least one linear or branched C₅-C₁₈ monocarboxylic acid selected from the group consisting of pentanoic acid, caproic acid, heptanoic acid, caprylic acid, nonanoic acid capric acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, oleic acid, palmitoleic acid and at least one linear or branched C₃-C₁₀ dicarboxylic acid selected from the group consisting of malonic acid, succinic acid, glutaric acid, adipic acid, heptanedioic acid, octananedioic acid, nonanedioic acid, decanedioic acid and at least one C₂-C₂₀ polyol having 2-10 hydroxyl group selected from the group consisting of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 1,3-butylene glycol, 2,3-butylene glycol neopentyl glycol, trimethylol propane, trimethylol ethane, pentaerythritol, sorbitol, and dipentaerythritol.
 28. The use according to claim 16 where the lubricant comprises at least 10 wt. % of the carboxylic acid ester.
 29. A method comprising lubricating an electric vehicle with a lubricant comprising a base oil selected from a carboxylic acid ester. 